Disorders of bone metabolism in which there is excessive resorption or remodelling of bone involving an imbalance between osteoclast (bone resorbing cells) and osteoblast (bone depositing cells) activity are widespread and include osteoporosis, Paget's disease of bone, and familial idiopathic hyperphosphatasemia. Bony metastases from malignant tumors are also a common feature of most forms of cancer and give rise to serious problems including severe pain, fractures, and hypercalcaemia.
Osteoporosis is a disorder of the skeleton associated with the loss of both hydroxyapatite (calcium phosphate complexes) and protein matrix (colloid). The result is thinning and weakening of the bones and an increased incidence of fractures, particularly compression fractures of the vertebrae and fractures of the hip and wrist from minimal trauma. In older patients it is called "senile osteoporosis" and affects both sexes. Coming after menopause it is referred to as "postmenopausal osteoporosis" and occurs in about one third of such women. Unfortunately, substantial bone loss must occur before it can be detected with routine radiographic procedures. There are a variety of current therapies for these disorders, none of which is accepted as adequately effective, and some of which have markedly adverse side effects. Hormonal therapies sometimes used for osteoporosis include androgens, estrogens, and calcitonin.
Many different methods of treatment have been tried with the aim of increasing bone density and substance. After several months of estrogen replacement in postmenopausal patients, for example, calcium balance becomes positive and bone resorption can decrease to normal. Thalassinos et al., Clin. Sci., 62, 221-226 (1982). The effects of estrogens in preventing postmenopausal bone loss are dose related. While the equivalent of 15 .mu.g of ethinyl estradiol daily can prevent vasomotor symptoms in menopause, doses of 15 to 25 .mu.g daily are required to prevent bone loss and 25 .mu.g or more per day can result in a net increase in bone density (Horsman et al., "The effect of estrogen dose on postmenopausal bone loss," N. Engl. J. Med., 309, 1405-1407 (1983). The positive effects of estrogen on calcium balance and bone density are reversed rapidly when treatment is discontinued Aloia et al., . "Risk factors for postmenopausal osteoporosis," Am. J Med , 78, 95-100 (1985). Chronic estrogen replacement therapy is increasingly recommended for postmenopausal women and can reduce the incidence of osteoporotic fractures. While earlier concerns over increased incidence of breast cancer are now reduced, there is a well documented increased risk of endometrial hyperplasia and uterine cancer. Martindale, The Extra Pharmacopoeia, Ed. James E. F. Reynold, page 1386 (London, The Pharmaceutical Press, 1989). Since most cases of osteoporosis occur in females, masculinizing side effects as well as adverse effects on liver function make the androgens an undesirable form of therapy. Injections, or nasal sprays, of salmon calcitonin or Elcatonin, a synthetic variant of eel calcitonin, are widely used in some countries in patients with osteoporosis, although clinical data supporting the utility is not universally accepted. See, e.g., Taggart, H. M. et al. Lancet, 1, 475 (1982); Tiegs, R. D. et al. New England Journal of Medicine, 312, 1097 (1985). One aspect of post-menopausal senile osteoporosis that may respond to calcitonin treatment is bone pain. Problems with calcitonin therapy, aside from the question of efficacy, include nausea, tingling, flushing, gastrointestinal disturbance, and disturbance of taste. Martindale, page 1339, supra. Also, formation of antibodies occurs. Other treatments for osteoporosis, including, calcium supplements, Vitamin D, and disphosphonates are sometimes used. However, thus far, their efficacy in established osteoporosis is not convincingly established. Salmon calcitonin is currently the medical treatment of choice in Paget's disease. Oxford Textbook of Medicine, Eds. Weatherall, Ledingham & Warrell, page 17.22. (Oxford Medical Publications, 2nd edition, 1987). Also, salmon calcitonin has shown benefit in bone metastasis, (Szanto J. and Sandor J., Clinical Trials J., 20, 266 (1983), though whether this is an action on bone or on the central nervous system is not yet certain. MacIntyre I., British Medical Bulletin, 42, 343 (1986). For hypercalcemic episodes from a variety of causes, intravenous or intramuscular injections of calcitonin can be an effective treatment, though the effect may be relatively short acting, Oxford Textbook of Medicine, page 10.68, supra, perhaps because of receptor down-regulation.
Thus, it will be appreciated that in each of these disorders of bone and calcium metabolism the existing therapies can have serious drawbacks in terms of efficacy and/or side effects.
British Patent Application 8709871, filed 27 Apr. 1987, described a novel peptide with the sequence: ##STR1##
The native molecule contains a disulfide bridge between the cysteine residues shown at positions 2 and 7 in the primary structure, is amidated at the 3' end, and is formed as a propeptide. Both of these post-translational modifications are required for full biologic activity. This peptide, now named amylin, was first isolated in the amyloid deposits in the pancreases of patients with Type 2 diabetes. Cooper et al., Proceedings of the National Academy of Sciences, U.S.A., 84, 8628 (1987). This peptide was discovered to have novel biological effects including enhancement of hepatic glucose output, increased production of lactate from skeletal muscle, and reduced action of insulin in skeletal muscle. See, e.g., Cooper et al., Biochem. Biophys. Acta, 1014, 247 (1989). Amylin is secreted from the beta cells of the islets of Langerhans in the pancreas in response to stimulation by glucose and amino acids, i.e., two food substrates. Amylin is said to be a partner anabolic hormone with insulin, among whose roles is the storage and disposal of food as carbohydrate and fat. Structurally and at the gene level, amylin has the characteristics of a peptide hormone, Cooper et al., ibid, and has homology to the neurotransmitter, calcitonin gene related peptide (CGRP), and to the hormone calcitonin. Cooper et al., ibid; Datta H. K., et al. Biochem. Biophys. Res. Commun., 162, 876 (1989).
This invention arises from the determination that, in addition to some structural homologies, amylin shares certain biological effects with calcitonin and has action on osteoclasts and other aspects of bone and calcium metabolism useful in the treatment of bone disorders and hypercalcaemia. MacIntyre, I., Lancet, 1989, Oct. 28, 1026. A linkage between amylin and bone and calcium metabolism had not been previously suggested, and the linkage between a pancreatic hormone responsive to food substrates and the regulation of bone resorption by osteoclasts was unexpected, as was the fact that amylin can be used for the control of plasma calcium.